[coroutines] Diagnose when 'main' is declared as a coroutine.

Summary: The title says it all.

Reviewers: rsmith, GorNishanov

Subscribers: mehdi_amini, cfe-commits

Differential Revision: https://reviews.llvm.org/D25078

llvm-svn: 282973

1 files changed, 5 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaCoroutine.cpp b/clang/lib/Sema/SemaCoroutine.cpp
index 51430360886..461ca8eddcf 100644
--- a/clang/lib/Sema/SemaCoroutine.cpp
+++ b/clang/lib/Sema/SemaCoroutine.cpp
@@ -127,6 +127,11 @@ checkCoroutineContext(Sema &S, SourceLocation Loc, StringRef Keyword) {
     S.Diag(Loc, diag::err_coroutine_constexpr) << Keyword;
   } else if (FD->isVariadic()) {
     S.Diag(Loc, diag::err_coroutine_varargs) << Keyword;
+  } else if (FD->isMain()) {
+    S.Diag(FD->getLocStart(), diag::err_coroutine_main);
+    S.Diag(Loc, diag::note_declared_coroutine_here)
+      << (Keyword == "co_await" ? 0 :
+          Keyword == "co_yield" ? 1 : 2);
   } else {
     auto *ScopeInfo = S.getCurFunction();
     assert(ScopeInfo && "missing function scope for function");